Sweetening of petroleum oils containing mercaptans with alkali and oxygen and then with alkali, a solutizer and oxygen



United States Patent'O SWEETENING OF PETROLEUM OILS CONTAININGMERCAPTANS WITH ALKALI AND OXYGEN AND THEN WITH ALKALI, A SOLUTIZER ANDOXYGEN Dorothy Sylvia Haresnape, formerly Macken, and Ronald LeonardDenyer, Sunbury-on-Thames, England, assignors to The British PetroleumCompany Limited No Drawing. Application June .20, 1952,.

Serial No. 294,722

Claims priority, application Great Britain July 4, 1951 I 6 Claims. (Cl.196-29) oils containing mercaptans.

' Among the processes which have been proposed for the removal ofmercaptans from petroleum oils is the socalled solutiser process whereinthe oils are contacted with an aqueouscaustic alkali solution containinga substance, such as an alkali metal phenolate or isobutyrate, capableof'increasing the solubility of the mercaptans in This inventionrelatesto the sweetening of petroleum the caustic solution. The causticsolution is regenerated According to the invention therefore, a processfor the sweetening of petroleum oils containing mercaptans, con sists intreating the oils with an aqueous caustic alkali solution containing asubstance which is capable of increasing thesolubilityof the inercaptansin the alkali,

solution, in the presence of oxygen or an oxygen-containing gas. Theaqueous caustic alkali solution containing the solubility promoter willheerinafter be referred to as the solutiser solution.

The mechanism of the sweetening operation appears to be that themercaptans first go from the oil phase to the aqueous phase, at whichstage both the mercaptan and total sulphur content of the oil arereduced. The mercaptans are oxidised in the aqueous phase, presumably tothe insoluble disulphides which then return to the oil phase, thusincreasing the sulphur content which gradually returns to its originalvalue while the mercaptan content drops to zero. The caustic solution isthus continuously regenerated so that no separate regeneration processis needed. It is to be understood that the scope of the invention is inno way limited by the above explanation of the mechanism of thereaction.

The treatment of the oil with the solutiser solution may advantageouslybe carried out in two or more stages, all in the presence of oxygen oran oxygen-containing gas.

It has been found that a considerable conversion of mercaptans todisulphides may be effected by means of an aqueous caustic alkalisolution alone, and it is therefore advantageous to treat the oil firstwith an aqueous caustic alkali solution containing no solubilitypromoter in the presence of oxygen or an oxygen-containing gas, and thenwith the solutiser solution likewise in the pres ence of oxygen or anoxygen-containing gas. This method of operation is more economical inthe use of solutiser solution and has the further advantage of reducingthe time of contact of the oil with th e solutiser solution and therebyconsiderably improving the colour of the prod uct.

It has been determined that the process of the invention is capable ofsweeteninga sour naphtha containing 0.05% by weight mercaptan sulphur.The contact time required is of the order of 20-30 minutes in atwo-stage process when giving the naphtha a 50/50 Wash with thesolutiser solution. Commercial cresol may conveniently be used as thesolubility promoter.

The invention will now be described by way of example asapplied to thecontinuous sweetening of an unrefined Iranian benzine having a boilingrange of l00-150 C and a mercaptan content of 0.05 weight percent.

Two runs were carried out, the first being a treatment with a solutisersolution consisting ofS N NaOH+L5 N cresol and the second with 5. Ncaustic soda alone. A blanket of oxygen was maintained above the liquidduring the whole'of the first run, and the total contact time wasinitially 30 minutes i. e. 15 in each stage, and was later reduced to 15minutes and finally to 10 minutes. It was found that with the longercontact times the product was orange in colour probably due: tooxidation products of the cresols. The results of this run are given inthe following table and indicate that a contact time of 20-30 minutes isrequired for a sweet product. The second run using 5 ,N NaOH alone wascarried out as a blank experiment; oxygen was again present initiallyand the total contact time was 30 minutes. For the first 16 hours theproduct was doctor. negative, but gradually became sour, and finallysettled down to a value of 0.002 per cent mercaptan. For the last fewhours, the oxygen blanket was replaced by air, the contact time stillremaining at 30 minutes. The mercaptan content of the product increasedalmost immediately, and after 4 hours had reached a value of 0.006 percent. These results are shown in the table.

TABLE Continuous Z-state washing of unrefined -150 C. Iranian benzineFeedstock:

Conditions:

Rate of feed of spirit... Spirit-reagent ratio Run No M Wash LiquidContact times:

1st stage 2nd stage Total (J0 at r- 1- cacao Oxygen feed Product from1st stage:

Mcrcaptan sulphur, wt. percent Product from 2nd stage:

Total sulphur wt. percent. Mereaptan sulphur, wt. percen Acidity ml.N/20NaOH/lOO ml Exlsteni; Gum mg./l00 ml 2 On On 0. 40 0. 40 trace trace 1in the absence of a catalyst for the oxidation of mercaptans todisulphides with an aqueous caustic alkali solution containing asubstance which is capable of increasing the solubility of themercaptans in the alkali solution, so as to effect a further conversionof mercaptans into disulphides, and separating a sweetened oil from thecaustic alkali solution.

2. A process. of sweetening. a petroleum oil containing mercaptans,which comprises mixing the oil with an aqueous caustic alkali solutionin the presence of, free oxygen so as to convert part of said mercaptansinto disulphides, separating the oil from, the caustic alkali solution,mixing the separated oil in the presence of free oxy gen but in theabsence of a catalyst for the oxidation of mercaptans to disulphideswith an aqueous caustic alkali solution containing a commercial cresolcapable of increasing the solubility of the mercaptans in the alkalisolution, so as to client a turther conversion of mercaptans intodisulphides, and separating a sweetened oil from the caustic alkali s luion.

3. A process of sweetening a petroleum oil containing mercaptans, whichcomprises mixing the oil with an aqueous caustic alkali solution in thepresence of free oxygen so as to convert part; of said mercaptans intodisulphides, separating the oil from the caustic alkali sohu tion,mixing the separated oil in the. presence of free oxygen but in theabsence of a. catalyst for the oxidation of mercaptans to disulphideswith an aqueous solution consisting of N NaQH+1.5 N commercial cresol soas to effect a further conversion of mercaptans into disulphides, andseparating a sweetened oil from the caustic alkali solution.

4. A process of sweetening a sour naphtha Containing more than 0.05%.weight of mercaptan sulphur, which comprises mixing the naphtha with anaqueous caustic alkali solution in the presence of free oxygen so as toconvert part of said mercaptans into disulphides, separating from thecaustic. alkali solution a naphtha containing not more than 0.05% weightmercaptan sulphur, mixing the separated naphtha in the presence of freeoxygen but in the absence of a catalyst for the oxidation of mercaptansto disulphides with an aqueous caustic alkali solution containing asubstance which is capable of increasing the solubility of themercaptans in the alkali solution, so as to effect a further conversionof mercaptans into disulphides, and separating a sweetened oil from thecaustic alkali solution.

5. A process of sweetening a sour naphtha containing more than 0.05%weight of mercaptan sulphur, which comprises mixing the naphtha with anaqueous caustic alkali solution in the presence of free oxygen so as toconvert part of said mercaptans into disulphides, separating from thecaustic alkali solution a naphtha containing not more than 0.05 weightmercaptan sulphur, mixing the separatednaphtha in the presence of freeoxygen but in the absence of a catalyst for the oxidation of necrcaptansto disulphides with an aqueous caustic alkali solution containing acommercial cresol capable of increasing the solubility of the mercaptansin the alkali solution, so as to effect a further conversion ofmercaptans into disulphides, and separating a sweetened 'oil from thecaustic alkali solution.

6. A process of sweetening a sour naphtha containing more than 0.05%weight of mercaptan sulphur, which comprises mixing the napht a with anaqueous caustic alkali solution in the presence of free oxygen so as toconvert part of said mercaptans into disulphides, separating from thecaustic alkali solution a naphtha containing not more than 0.05% weightmercaptan sulphur, mixing the separated naphtha in the presence of freeoxygen but in the absence of a catalyst for the oxidation of mercaptansto disulphides with an aqueous, solution consisting of '5 N NaOH+1.5 Ncommercial cresol so as to efiect a further conversion of mercaptansinto disulphides, and separating a sweetened oil from the caustic alkalisolution.

References Cited in the file of this patent UNITED STATES PATENTS2,413,945 Bolt Jan. 7, 1947 2,427,212 Henderson Sept. 9, 1947 2,474,028Berger June 21, 1949 2,552,399 Browder' May 8, 1951 2,638,439 Browder etal. May 12, 1953 FOREIGN PATENTS 471,373 Canada Feb. 6, 1951 475,538Canada July 24, 1951 629,914 Great Britain Sept. 30, 1949

1. A PROCESS OF SWEETENING A PETROLEUM OIL CONTAINING MERCAPTANS, WHICHCOMPRISES MIXING THE OIL WITH AN AQUEOUS CAUSTIC ALKALI SOLUTION IN THEPRESENCE OF FREE OXYGEN, SO AS TO CONVERT PART OF SAID MERCAPTANS INTODISULPHIDES, SEPARATING THE OIL FROM THE CAUSTIC ALKALI SOLUTION, MIXINGTHE SEPARATED OIL IN THE PRESENCE OF FREE OXYGEN BUT IN THE ABSENCE OF ACATALYST FOR THE OXIDATION OF MERCAPTANS TO DISULPHIDES WITH AN AQUEOUSCAUSTIC ALKALI SOLUTION CONTAINING A SUBSTANCE WHICH IS CAPABLE OFINCREASING THE SOLUBILITY OF THE MERCAPTANS IN THE ALKALI SOLUTION, SOAS TO EFFECT A FURTHER CONVERSION OF MERCAPTANS INTO DISULPHIDES, ANDSEPARATING A SWEETENED OIL FROM THE CAUSTIC ALKALI SOLUTION.